The random access process is an important process in radio communication system as well as an important phase in radio access process. In the TD-SCDMA radio communication system which is one of the third generation mobile communication systems, the random access process also includes an important uplink synchronization process.
The TD-SCDMA system adopts the technology of time division synchronization code division multiple access and it has a high demand for the uplink and downlink synchronization, especially for the uplink synchronization. In the TD-SCDMA system, uplink pilot time slot (UpPTS) and uplink synchronization code (SYNC_UL) are specifically defined to be used in uplink synchronization.
In the TD-SCDMA system, the random access process is a physical layer process, in which, an important step is to select the uplink synchronization code and its transmitting moment in UpPTS. This selection process is not only required by the uplink synchronization process, but more importantly, it is also the essence of random access process; this selection process is a concentrated reflect of the distribution method of competition sharing for the uplink common channel resource, i.e. physically random access channel (PRACH), in the random access process.
In the TD-SCDMA system, one cell is configured with eight uplink synchronization codes numbered of 0-7. During the random access process, the uplink synchronization code is also described as signature. During the random access process, if the user equipments (UE) select the same signature and transmit the signature at the same moment, namely in the UpPTS time slot of the same sub-frame, conflict will be generated and no response from the base station will be received, thereby causing the failure of the random access process.
For the TD-SCDMA system, in the broadcast message of the latest protocol “3GPP TS 25.331 V6.4.0”, the configuration of the signature and UpPTS time slot resource (i.e. the transmission moment in the UpPTS time slot) is realized by Access Service Class (ASC) configuration information unit whose schematic structure is shown in FIG. 1, in which, available uplink synchronization codes (namely the signature), the number of sub-channels and available sub-channels are configured corresponding to each ASC value, the sub-channel is exactly the UpPTS time slot resource. In this method of configuration, the signature and the UpPTS time slot resource are configured as two independent resources.
In TD-SCDMA system, by way of defining different ASCs with each ASC configured with corresponding resources, different access service qualities are realized. In the TD-SCDMA system, there are totally eight classes of ASCs configured, from class 0 to class 7, and the resources configured for each ASC by the system include the UpPTS time slot resource and the signature used in the random access process. Meanwhile, on the UE side, the system defines totally sixteen classes of ACs (Access Class), from class 0 to class 15, and for each UE, one or more ACs can be configured. In the system broadcast message, the system broadcasts to the UE the number of configured ASCs, the signature that is configured for each ASC, and the UpPTS time slot resource, as well as the corresponding relationship between AC and ASC. The radio resource control (RRC) layer of the UE determines the corresponding ASC value based on the corresponding relationship and the configured AC value thereof, and configures the ASC value and other corresponding related resources to the media access layer. At the same time, the RRC layer of the UE configures the corresponding signature of each ASC and the UpPTS time slot resource to the physical layer. However, there is still no solution in the existing technology in respect to how the UE physical layer selects the resource configured by the system for the ASC in order to meet the QoS requirements and avoid the generation of conflicts by all means.